Downhole fluid pressure pulse generator

ABSTRACT

A fluid pressure pulse generator forms part of a tubing string for use in a wellbore. The generator includes a tubular stator and a tubular rotor disposed for rotation within the stator to periodically align rotor transverse openings with stator transverse openings to permit fluid communication from a rotor longitudinal bore to a stator outer surface. The rotor is disposed longitudinally between bearing members to define a pair of end gaps sized for creation of end fluid film bearings. The stator inner surface defines a plurality of longitudinally extending grooves. The rotor transverse openings are adapted to direct fluid away from the rotor longitudinal bore in a direction having a tangential component in respect to the rotor longitudinal bore, and into the grooves. The stator transverse openings are adapted to direct away from the stator outer surface in at least six different directions.

FIELD OF THE INVENTION

The present invention relates to oil and gas production from wellbores, and more particularly to a fluid pressure pulse generator and methods of using the same.

BACKGROUND OF THE INVENTION

In the field of oil and gas production, fluid pressure pulse generators are used to stimulate produced fluids from a wellbore, enhance cleaning of the wellbore, and enhance injection sweeps in the wellbore. A typical pulse generator is connected to a tubing string, whether made of pipe segments or coiled tubing. The pulse generator includes a tubular stator, a tubular rotor, and an external motor (e.g., a submersible well motor) that drives rotation of the rotor within the stator to periodically align transverse openings defined by them. Fluid is pumped down the tubing string and exits transversely through the periodically aligned openings into the wellbore, thereby creating a fluid pressure pulse in the wellbore.

One limitation associated with pulse generators is that high fluid pressure acting on the rotor increases the bearing force of the rotor on its bearing surfaces. This increases the rotational friction acting on the rotor, which impedes rotation of the rotor and accelerates wear of the rotor and the bearing surfaces. Another limitation is that the mechanical coupling between the external motor and the rotor may degrade or fail. Another limitation is that the stator typically has pulse openings that emit fluid pressure pulses in only one or two transverse directions, which may limit the pulse generator's efficacy for certain applications.

SUMMARY OF THE INVENTION

The present invention comprises a fluid pressure pulse generator for forming part of a tubing string for use in a wellbore. The fluid pressure pulse generator comprises a tubular stator and a tubular rotor disposed for rotation within the stator to periodically align at least one rotor transverse opening with at least one stator transverse opening to permit fluid communication from a rotor longitudinal bore to a stator outer surface.

In one aspect, a fluid pressure pulse generator comprises a pair of longitudinally spaced apart annular bearing members, wherein each of the bearing members comprises an annular bearing surface, and defines a bearing member opening for fluid communication with the tubing string. The rotor is disposed longitudinally between the bearing members with the rotor longitudinal bore in fluid communication with the bearing member openings. Each rotor longitudinal end and a bearing surface define an end gap which is in fluid communication with the bearing member openings and sized for creation of end fluid film bearings.

In one embodiment, the fluid pressure pulse generator also comprises a pair of crossover subs adapted for connecting the stator to the tubing string. Each bearing member is disposed longitudinally between and in abutting relationship with one of the subs and one of the stator longitudinal ends.

In one embodiment, the fluid pressure pulse generator also comprises a pair of longitudinally spaced apart annular bushings. Each bushing is disposed in an annular space defined between a stator inner surface and a rotor outer surface. The rotor outer surface and bushing inner surfaces define therebetween a pair of inner annular gaps in fluid communication with the bearing member openings and sized for creation of inner annular fluid film bearings. The stator inner surface and bushing outer surfaces may define therebetween outer annular gaps in fluid communication with the bearing member openings and sized for creation of outer annular fluid film bearings. The end gaps may extend between bushing longitudinal ends and the bearing surfaces.

In another aspect, the pulse generator comprises a stator having an inner surface which defines a plurality of longitudinally extending grooves. The at least one rotor transverse opening is adapted to direct fluid away from the rotor longitudinal bore in a direction having a tangential component in respect to the rotor longitudinal bore. The rotor is disposed for rotation within the stator to periodically align the at least one rotor transverse opening with the at least one stator transverse opening, followed sequentially by alignment of the at least one rotor transverse opening with the grooves.

In another aspect, the at least one stator transverse opening includes at least four or six stator transverse openings. The at least four or six stator transverse openings are adapted to direct away from the stator outer surface in at least four or six different directions.

In one embodiment, the at least one rotor transverse openings comprises at least one pair of rotor transverse openings. The pair of transverse openings are positioned on the rotor such that rotation of the rotor within the stator aligns the pair of rotor transverse openings simultaneously with a pair of the at least four or six stator transverse openings.

In one embodiment, each of the stator transverse openings has a different longitudinal position on the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings shown in the specification, like elements may be assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention.

FIG. 1 shows a top perspective view of an embodiment of the pulse generator of the present invention.

FIG. 2 shows an exploded top perspective view of the pulse generator of FIG. 1.

FIG. 3 shows a cross-sectional view of the pulse generator of FIG. 1 along its longitudinal midline.

FIG. 4 shows the uphole portion of FIG. 3 at an enlarged scale.

FIG. 5 shows a top view of the stator of the pulse generator of FIG. 1.

FIG. 6 shows a cross-sectional view of the stator of FIG. 5 along longitudinal section line A-A of FIG. 5.

FIG. 7 shows an elevation view of the stator of FIG. 5 from the perspective of line B-B of FIG. 5.

FIG. 8 shows an elevation view of the stator of FIG. 5 from the perspective of line C-C of FIG. 5.

FIG. 9 shows a top view of the rotor of the pulse generator of FIG. 1.

FIG. 10 shows a cross-sectional view of the rotor of FIG. 9 along longitudinal section line A-A of FIG. 9.

FIG. 11 shows a cross-sectional view of the rotor of FIG. 10 along transverse section line B-B of FIG. 10.

FIG. 12 shows a cross-sectional view of the rotor of FIG. 10 along longitudinal section line C-C of FIG. 10.

FIG. 13 shows a side elevation view of the pulse generator of FIG. 1 in a tubing string in a wellbore.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Definitions

Any term or expression not expressly defined herein shall have its commonly accepted definition understood by a person skilled in the art.

As used herein, “longitudinal” means aligned with the axial direction of tubular elements associated with the invention, and “transverse” means a direction that is substantially perpendicular to the longitudinal direction.

As used herein “uphole” and “downhole” are used to describe relative longitudinal positions of parts in the wellbore. One skilled in the art will recognize that wellbores may not be strictly vertical or horizontal, and may be slanted or curved in various configurations. Therefore, the longitudinal direction may or may not be vertical (i.e., perpendicular to the plane of the horizon), and the transverse direction may or may not be horizontal (i.e., parallel to the plane of the horizon). Further, an “uphole” part may or may not be disposed above a “downhole” part.

As used herein, “fluid” means either a liquid, a liquid mixed with solids and/or entrained gases, or a gas. Non-limiting examples of fluids that may be used in conjunction with the present invention include drilling fluids conventionally referred to as “drilling mud”, and nitrogen gas.

As used herein, “tubing string”, refers to any tubular structure in a wellbore that may be used to convey fluid in a wellbore. Non-limiting examples of tubing string include rigid pipe segments, and coiled tubing.

Pulse Generator.

FIGS. 1 to 4 show an embodiment of a fluid pressure pulse generator (10) of the present invention. In this embodiment, the pulse generator (10) includes a tubular stator (20), a tubular rotor (40), annular bushings (60), annular washers (80), annular bearing members (100), O-ring gaskets (120), and crossover subs (140). In this embodiment, the uphole bushing (60 a), washer (80 a), annular bearing member (100 a), O-ring gasket (120 a) and crossover sub (140 a) are the same as the corresponding downhole components (60 b, 80 b, 100 b, 120 b, 140 b), such that this embodiment of the fluid pressure pulse generator (10) is substantially symmetric about its longitudinal center.

Stator.

The stator (20) defines a stator longitudinal bore (28) (FIG. 6) that receives the rotor (40), the bushings (60), and washers (80). The stator (20) also defines stator transverse openings (32) that permit fluid communication from the rotor transverse openings (52) (FIGS. 10 to 12), when aligned with the stator transverse openings (32), to outside of the stator (20).

In one embodiment, as shown in FIGS. 5 to 8, the stator (20) is made of stainless steel (e.g., American Iron and Steel Institute (AISI) grade 4330 or 4340 alloy steel) and is in the form of a cylindrical tubular member having a total longitudinal length of about 4.125 inches and an outer diameter of about 1.7 inches. The length and diameter may be varied in different embodiments. In this embodiment, as shown in FIG. 6, the stator (20) is formed from a stator inner mandrel (22) surrounded by a stator outer sleeve (24). The stator inner mandrel (22) has a stator inner surface (26) that defines the stator longitudinal bore (28). The stator outer sleeve (24) defines a stator outer surface (30). In other embodiments, the stator (20) may be formed from one piece rather than from the stator inner mandrel (22) and the stator outer sleeve (24).

In this embodiment, the stator (20) defines six stator transverse openings (32 a to 32 f) permitting fluid communication from the stator inner surface (26) to the stator outer surface (30). Each stator transverse opening (32) has a diameter of about 7/32 inches (0.219 inches) at the stator outer surface (30). The angular distance between adjacent stator transverse openings (32) is about 60 degrees. Stator transverse openings (32 a, 32 d) are separated by about 180 degrees from each other. In general, the stator transverse openings (32) have a diameter of about 0.219 inches at the stator inner surface 926), except that stator transverse openings (32 a, 32 d) have an enlarged diameter of about 0.600 inches at the stator inner surface (26) to accommodate fluid exiting the rotor radial openings (52 a, 52 b, 52 c) tangentially to the rotor longitudinal bore (44) as discussed below. Stator transverse openings (32 a, 32 d) are positioned at about the longitudinal center of the stator (20). Stator transverse opening (32 b) is about 0.424 inches below the longitudinal center of the stator (20). Stator transverse opening (32 c) is about 0.812 inches above the longitudinal center of the stator (20). Stator transverse opening (32 e) is about 0.813 inches below the longitudinal center of the stator (20). Stator transverse opening (32 f) is about 0.408 inches above the longitudinal middle of the stator (20). In other embodiments, the stator (20) may have a different number and arrangement of stator transverse openings (32).

In this embodiment, as shown in FIG. 5, the stator inner surface (26) has a grooved portion (34) which defines a plurality of elongate grooves that extend longitudinally for about 0.30 inches on either side of the longitudinal center of the stator (20). It will be understood that the grooved portion (34) extends around the stator inner surface (26) to the longitudinal cross-section opposite to that shown in FIG. 5. The grooved portion (34) enhances rotation of the rotor (40) within the stator longitudinal bore (28), as described below.

Rotor.

The rotor (40) defines rotor transverse openings (52) that permit fluid communication from the rotor longitudinal bore (44) to the stator transverse openings (32) when the rotor transverse openings (52) are aligned with the stator transverse openings (32). In embodiments, some or all of the stator transverse openings (32) also permit fluid communication from the rotor longitudinal bore (44) to the grooved portion (34) of the stator inner surface (26).

In one embodiment, as shown in FIGS. 9 to 12, the rotor (40) is made of stainless steel (e.g., AISI grade 4330 or 4340 alloy steel), and is in the form of a cylindrical tubular member having a total longitudinal length which is just slightly shorter than the total length of the stator (20), as discussed below. The rotor (40) has a rotor inner surface (42) defining a rotor longitudinal bore (44), and a rotor outer surface (46). A rotor middle portion (48) fits within close tolerance of the stator inner surface (26) without preventing rotation of the rotor (40) within the stator longitudinal bore (28). In comparison with the rotor middle portion (48), the rotor end portions (50 a, 50 b) have a reduced outer diameter so that they and the stator inner surface (26) define an annular space therebetween for the bushings (60 a, 60 b) and washers (80 a, 80 b), as may be seen in FIGS. 3 and 4.

In this embodiment, the rotor (40) defines three rotor transverse openings (52 a, 52 b, 52 c) permitting fluid communication from the rotor inner surface (42) to the rotor outer surface (46). The rotor transverse openings (52 a, 52 b, 52 c) may have a diameter of about 5/64 inches (0.078 inches). The angular distance between adjacent rotor transverse openings (52 a, 52 b, 52 c) is about 120 degrees. As shown in FIG. 11, the rotor transverse openings (52 a, 52 b, 52 c) are adapted to direct fluid away from a rotor longitudinal bore (44) in a direction having a tangential component relative to the rotor longitudinal bore (44) so that fluid flowing from the rotor longitudinal bore (44) through the rotor transverse openings (52 a, 52 b, 52 c) causes the rotor (40) to rotate. In this embodiment, the rotor transverse openings (52 a, 52 b, 52 c) are oriented tangentially to the rotor longitudinal bore (44). However, the rotor transverse openings (52 a, 52 b, 52 c) may be adapted to direct fluid away from a rotor longitudinal bore (44) in a direction having a tangential component relative to the rotor longitudinal bore (44), so long as the rotor transverse openings (52 a, 52 b, 52 c) direct fluid in a direction that is non-perpendicular to the rotor outer surface (46). In other embodiments, the rotor (40) may be driven by a motor mechanically coupled to the rotor (40). The rotor transverse openings (52 a, 52 b, 52 c) are positioned at about the longitudinal center of the rotor (40). Accordingly, the rotor transverse openings (52 a, 52 b, 52 c) will periodically align, one at a time, with one of the stator transverse openings (32 a, 32 d) and the grooved portion (34) of the stator inner surface (26) as the rotor (40) rotates within the stator longitudinal bore (28).

In this embodiment, the rotor (40) also defines four rotor transverse openings (52 d, 52 e, 52 f, 52 g) permitting fluid communication from the rotor inner surface (42) to the rotor outer surface (46). The rotor transverse openings (52 d, 52 e, 52 f, 52 g) have a diameter of about 3/16 inches (0.188 inches). The angular distance between adjacent ones of the rotor transverse openings (52 d, 52 e, 52 f, 52 g) is about 90 degrees, with rotor transverse opening 52(d) being in angular alignment with the rotor transverse opening (52 a) on the rotor outer surface (46).

In this embodiment, the rotor transverse opening (52 d) is longitudinally aligned with the stator transverse opening (32 c), and rotor transverse opening (52 g) is longitudinally aligned with stator transverse opening (32 e). The angular distance between rotor transverse openings (52 d, 52 g) is about 180 degrees, and the angular distance between stator transverse openings (32 c, 32 e) is also about 180 degrees. Accordingly, periodic alignment of openings (32 c, 52 d) will coincide with periodic alignment of openings (32 e, 52 g), as the rotor (40) rotates within the stator longitudinal bore (28).

In this embodiment, the rotor transverse opening (52 e) is longitudinally aligned with the stator transverse opening (32 f). The rotor transverse opening (52 f) is longitudinally aligned with stator transverse opening (32 b). The angular distance between rotor transverse openings (52 e, 52 f) is about 180 degrees, and the angular distance between stator transverse openings (32 f, 32 b) is also about 180 degrees. Accordingly, periodic alignment of openings (32 f, 52 e) will coincide with periodic alignment of openings (32 b, 52 f), as the rotor (40) rotates within the stator longitudinal bore (28).

Bushings and Washers.

In one embodiment, the bushings (60) provide annular and end bearing surfaces for the rotor (40). The washers (80) avoid direct frictional contact between the end bearing surfaces of the bushings (60) and the rotor (40).

In one embodiment, as shown in FIGS. 2 to 4, the annular bushings (60) are made of a suitably durable and low-friction polymer material, such as polyether ether ketone (PEEK), and are in the form of a cylindrical tubular member, which may have a longitudinal length of about 0.935 inches. PEEK is advantageous as it is known to exhibit excellent chemical resistance, low permeability, and low moisture absorption.

The washers (80) may also be made of a suitable polymer or metal. In one embodiment, the washers (80) are made of stainless steel (e.g., Nitronic™ alloy (AK Steel, West Chester Township, Ohio, United States)), and may have a longitudinal dimension (thickness) of about 0.062 inches.

FIG. 4 shows the uphole portion of the fluid pressure pulse generator (10) at an enlarged scale. It will be understood that the downhole portion of the pulse generator is substantially the same, but as a mirror image. In this embodiment, after the rotor (40) is inserted in the stator longitudinal bore (28), the washers (80) are inserted into the stator longitudinal bore (28) in abutting relationship with the shoulder of the rotor (40) formed at the junction of the rotor middle portion (48) and one of the rotor end portions (50). Subsequently, the bushings (60) are inserted into the stator longitudinal bore (28) in abutting relationship with the washers (80).

Annular Bearing Member, O-Ring Gaskets, and Crossover Subs.

The uphole annular bearing member (100 a) defines an uphole annular bearing member opening (102 a) that permits fluid communication between an uphole portion of a tubing string into the rotor longitudinal bore (44). The downhole annular bearing member (100 a) defines a downhole annular bearing member opening (102 a) that permits fluid communication between the rotor longitudinal bore (44) and a downhole portion of a tubing string. The bearing members (100) also define annular bearing surfaces (104 a) in relation to the end of the rotor (40), as shown in FIG. 4. In one embodiment, the annular bearing members (100) are made of stainless steel (e.g., Nitronic™ alloy). The outer periphery of the annular bearing member (100 a) abuts against the end of the stator (20). The annular bearing member (100 a) has a central tubular portion that extends into the rotor longitudinal bore (44) for fluid communication between the crossover sub bore (142 a) and the rotor longitudinal bore (44) via the bearing member opening (102 a).

The O-ring gasket (120 a) seals between the annular bearing member (100 a) and the crossover sub (140 a), so as to prevent fluid flow between the interfacing surfaces, and are made of a suitable elastomer (e.g. rubber, or Viton75™ fluorocarbon elastomer; DuPont Company, Wilmington, Del., United States). In this embodiment, the gasket (120 a) is received in an annular grooves defined by the annular bearing member (100 a).

The crossover subs (140) connect the stator (20) to uphole and downhole portions of a tubing string, and define a crossover sub bore (142) permitting fluid communication between the tubing string portions to the rotor longitudinal bore (44) via the annular bearing member openings (102). In one embodiment, the crossover subs (140) are made of stainless steel (e.g., AISI grade 4330 or 4340 alloy steel), and are in the form of a cylindrical tubular members. Each crossover sub (140) has a threaded “box” end for attachment to a complementary threaded “pin” end of the stator (20), and a threaded “pin” end for attachment to a complementary threaded “box” end of a tubing string.

In this embodiment, after the bushings (60) are inserted into the stator longitudinal bore (28), the annular bearing members (100) and O-ring gaskets (120) are placed into the “box” end of the crossover subs (140). The threaded “box” ends of the crossover subs (140) are then screwed tightly onto the threaded “pin” ends of the stator (20), so that the O-ring gaskets (120) create a fluid-tight seal at the interfacing and abutting surfaces of the annular bearing members (100) and the crossover subs (140).

Fluid Film Bearings.

In embodiments of the present invention, the device is configured with at least one fluid bearing, created by gaps between adjacent surfaces. Preferably, the gap is less than about 0.01 inches, and more preferably less than about 0.008 inches. FIG. 4 shows a cross-sectional view of an uphole portion of the pulse generator of FIG. 1, at an enlarged scale relative to FIG. 3. Again, it will be understood that the downhole portion of the pulse generator is substantially the same, but longitudinally inverted. In this embodiment of the pulse generator (10), the total length of the stator (20) is 4.125 inches, whereas the total length of the rotor (40) is about 4.119 inches, for a difference in length of about 0.006 inches. Preferably, this difference in length is less than about 0.01 inches, and more preferably less than about 0.008 inches. Accordingly, when the rotor (40) is longitudinally centered within the stator longitudinal bore (28), the rotor (40) and the bushing (80) are separated from the annular bearing surface (104) of the bearing member (100) by an end gap (160 a) having a longitudinal length of about 0.003 inches. The size of the gap (160 a) in FIG. 4 has been exaggerated for clarity and is not shown to scale. Fluid under pressure can flow into the end gap (160 a) to form a thin film of pressurized fluid that separates the rotor (40) and bushing (60 a) from the annular bearing surface (104) of the annular bearing member (100). This thin film of pressurized fluid provides a fluid film bearing for the rotor (40) and bushing (60 a). In other embodiments, the size of the gap (160 a) may be different. A person skilled in the art may be able to determine the size of the gap needed to create a fluid film bearing having regard to the mechanical properties and pressure of a particular fluid. In the embodiment shown in FIG. 4, the inner diameter of the annular bushing (60 a) and the washer (80 a) are thousandths of an inch greater than the outer diameter of the rotor end portion (50 a) to create an inner annular gap (162 a) therebetween. Their outer diameters are thousandths of an inch less than the diameter of the portion of the stator inner bore (28) in which they reside to create an annular outer gap (164 a) therebetween. In use, the inner annular gap (162 a) and outer annular gap (162 a) allow for the creation of an inner annular fluid film bearings, and an outer annular fluid film bearing, respectively. Further, as shown in FIG. 4, the combined longitudinal length of the bushing (60 a) and the washer (80 a) may be thousands of an inch less than the longitudinal distance between the annular bearing surface (104) and the shoulder of the rotor (40), such that fluid film bearings may also be created between these parts.

Use and Operation.

FIG. 13 shows an exemplary use of the pulse generator (10) of the present invention to stimulate a wellbore (200). The pulse generator (10) is connected to uphole and downhole portions of a tubing string (202) by the crossover subs (140). The uphole portion of the tubing string (202) is connected to a pump (204) that pressurizes fluid (e.g., drilling fluid or nitrogen gas) down the tubing string (202) and into the rotor longitudinal bore (44) so that the fluid pressure inside the rotor longitudinal bore (44) is higher than the fluid pressure in the wellbore (200).

Accordingly, fluid flows from the rotor longitudinal bore (44) out of the rotor transverse openings (52 a to 52 e). Flow of fluid out of the rotor transverse openings (52 a, 52 b, 52 c) causes the rotor (40) to rotate within the stator longitudinal bore (28) on account of these openings being oriented tangentially to the rotor longitudinal bore (40). Impingement of the fluid exiting rotor transverse openings (52 a, 52 b, 52 c) on the grooved portion (34) enhances this rotational effect by allowing some fluid to exit the rotor transverse openings (52 a, 52 b, 52 b) regardless of the angular position of the rotor (40) relative to the stator (20).

When one of the rotor transverse openings (52 a to 52 e) aligns with one of the stator transverse openings (32 a to 32 f), a pulse of fluid flows from the rotor longitudinal bore (44) through the aligned openings to outside of the stator (20) to create a fluid pressure pulse in the wellbore. The frequency of the pulses depends on the rotational speed of the rotor (40) within the stator (20). The amplitude of the pulses depends on the pressure differential between the pressure in the rotor longitudinal bore (44) and the portion of the wellbore proximate to the apparatus (10). In the embodiment of the pulse generator (10) shown in the Figures, the provision of six stator transverse openings (32 a to 32 f) with equal angular spacing between them allows for the creation of pulses that effectively surround the stator (20).

The pressurized fluid also flows into the end gap (160 a) (FIG. 4) to create a fluid film bearing between the rotor (40) and the bushing (60), and the annular bearing surface (104) of annular bearing member (100). Such a fluid bearing is created at the uphole end of the rotor (40) which tends to push the rotor (40) in the downhole direction, and another such fluid bearing is created at the downhole end of the rotor (40) which tends to push the rotor (40) in the uphole direction. Accordingly, any momentary increase of fluid pressure acting on the uphole end of the rotor (40) that pushes the rotor (40) downwards will be accompanied by a reduction of the size of the downhole end gap (160). This reduction in size of the downhole end gap (160) will be accompanied by a momentary increase the fluid pressure therein, thus pushing the rotor (40) in the uphole direction. Accordingly, the uphole and downhole fluid bearings will tend to maintain the rotor (40) in an equilibrium position in which the uphole and downhole ends of the rotor (40) do not contact the annular bearing surface (104) of the annular bearing member (100). This avoids direct rotational friction between the rotor (40) and the annular bearing surface (104) of the annular bearing member (100), allowing the rotor (40) to rotate freely, which in turn allows for reliable generation of fluid pressure pulses under varying fluid flow and pressure conditions. As fluid flows through the pulse generator (10) from the uphole end to the downhole end, fluid film bearings are likewise created in the gaps between the bushing (60) and the washer (80), between the bushing (60) and the stator inner surface (26), between the bushing (60) and the rotor outer surface (46), between the washer (80) and the stator inner surface (26), and between the washer (80) and the rotor outer surface (46).

The pulse generator may be used in any scenario where pulsed fluid jets are desirable or required downhole in a wellbore. For example, the pulse generator may be used to stimulate hydrocarbon flow from formations bearing oil and gas, clean out sand, scale or other impediments to fluid flow in a tubular or in a formation, or clean out or reopen ports or openings in a tubular, such as a frac port.

Interpretation.

References in the specification to “one embodiment”, “an embodiment”, etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as “solely,” “only,” and the like, in connection with the recitation of claim elements or use of a “negative” limitation. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

The singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. The term “and/or” means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase “one or more” is readily understood by one of skill in the art, particularly when read in context of its usage.

The term “about” can refer to a variation of ±5%, ±10%, ±20%, or ±25% of the value specified. For example, “about 50” percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term “about” can include one or two integers greater than and/or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term “about” is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

As will also be understood by one skilled in the art, all language such as “up to”, “at least”, “greater than”, “less than”, “more than”, “or more”, and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims appended to this specification are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. 

1. A fluid pressure pulse generator for forming part of a tubing string for use in a wellbore, the fluid pressure pulse generator comprising: (a) a pair of longitudinally spaced apart annular bearing members, wherein each of the bearing members comprises an annular bearing surface, and defines a bearing member opening for fluid communication with the tubing string; and (b) a tubular stator and a tubular rotor disposed for rotation within the stator to periodically align at least one rotor transverse opening with at least one stator transverse opening to permit fluid communication from a rotor longitudinal bore to a stator outer surface; (c) wherein the rotor is disposed longitudinally between the bearing members with the rotor longitudinal bore in fluid communication with the bearing member openings, and wherein rotor longitudinal ends and the bearing surfaces define therebetween a pair of end gaps in fluid communication with the bearing member openings and sized for creation of end fluid film bearings.
 2. The fluid pressure pulse generator of claim 1, further comprising a pair of crossover subs adapted for connecting the stator to the tubing string, and wherein each bearing member is disposed longitudinally between and in abutting relationship with one of the subs and one of the stator longitudinal ends.
 3. The fluid pressure pulse generator of claim 1, further comprising a pair of longitudinally spaced apart annular bushings, wherein each bushing is disposed in an annular space defined between a stator inner surface and a rotor outer surface, and wherein the rotor outer surface and bushing inner surfaces define therebetween a pair of inner annular gaps in fluid communication with the bearing member openings and sized for creation of inner annular fluid film bearings.
 4. The fluid pressure pulse generator of claim 1, wherein the stator inner surface and bushing outer surfaces define therebetween outer annular gaps in fluid communication with the bearing member openings and sized for creation of outer annular fluid film bearings.
 5. The fluid pressure pulse generator of claim 3, wherein the end gaps extend between bushing longitudinal ends and the bearing surfaces.
 6. A fluid pressure pulse generator for forming part of a tubing string for use in a wellbore, the fluid pressure pulse generator comprising: (a) a tubular stator defining at least one stator transverse opening, and comprising a stator inner surface defining a plurality of longitudinally extending grooves; and (b) a tubular rotor defining at least one rotor transverse opening adapted to direct fluid away from a rotor longitudinal bore in a direction having a tangential component in respect to the rotor longitudinal bore, wherein the rotor is disposed for rotation within the stator to periodically align the at least one rotor transverse opening with the at least one stator transverse opening to permit fluid communication from the rotor longitudinal bore to an outer surface of the stator, followed sequentially by alignment of the at least one rotor transverse opening with the grooves.
 7. A fluid pressure pulse generator for forming part of a tubing string for use in a wellbore, the fluid pressure pulse generator comprising a tubular stator and a tubular rotor disposed for rotation within the stator to periodically align at least one rotor transverse opening with at least six stator transverse openings to permit fluid communication from a rotor longitudinal bore to a stator outer surface, wherein the at least six stator transverse openings are adapted to direct away from the stator outer surface in at least six different directions.
 8. The fluid pressure pulse generator claim 7, wherein the at least one rotor transverse openings comprises at least one pair of rotor transverse openings, wherein the pair of transverse openings are positioned on the rotor such that rotation of the rotor within the stator aligns the pair of rotor transverse openings simultaneously with a pair of the at least six stator transverse openings.
 9. The fluid pressure pulse generator of claim 7, wherein each of the stator transverse openings has a different longitudinal position on the stator. 